Re: [RESEND PATCH V5 6/7] ublk_drv: add START_USER_RECOVERY and END_USER_RECOVERY support

[Ming Lei <ming.lei@redhat.com>]

On Fri, Sep 23, 2022 at 02:15:04PM +0800, ZiyangZhang wrote:
> START_USER_RECOVERY and END_USER_RECOVERY are two new control commands
> to support user recovery feature.
> 
> After a crash, user should send START_USER_RECOVERY, it will:
> (1) check if (a)current ublk_device is UBLK_S_DEV_QUIESCED which was
>     set by quiesce_work and (b)chardev is released
> (2) reinit all ubqs, including:
>     (a) put the task_struct and reset ->ubq_daemon to NULL.
>     (b) reset all ublk_io.
> (3) reset ub->mm to NULL.
> 
> Then, user should start a new process and send FETCH_REQ on each
> ubq_daemon.
> 
> Finally, user should send END_USER_RECOVERY, it will:
> (1) wait for all new ubq_daemons getting ready.
> (2) update ublksrv_pid
> (3) unquiesce the request queue and expect incoming ublk_queue_rq()
> (4) convert ub's state to UBLK_S_DEV_LIVE
> 
> Note: we can handle STOP_DEV between START_USER_RECOVERY and
> END_USER_RECOVERY. This is helpful to users who cannot start new process
> after sending START_USER_RECOVERY ctrl-cmd.
> 
> Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming